1. Field of the Invention
This invention relates to a cathode for use in electrolysis and to a method for production of the cathode. More specifically, it relates to a cathode which has superior corrosion resistance and a low hydrogen evolution potential and which is suitable for electrolysis of sodium chloride by an ion exchange membrane and to a method for the production of the cathode.
2. Description of the Prior Art
In recent years, the role of cathodes has been considered to be important as in the case of anodes in an electrolytic apparatus for producing hydrogen, sodium hydroxide, chlorine, etc. by electrolyzing an aqueous solution, such as an aqueous solution of sodium chloride.
Iron and mild steel in the form of, for example, a plate, a screen or a perforated plate, have been frequently used as cathodes for use in electrolysis of this kind. Iron is an inexpensive cathode material and has a quite low hydrogen evolution potential. Various activated cathodes obtained by coating iron with various substances to improve its properties are known.
Conventional techniques for providing such activated cathodes include, for example, a method comprising coating a sacrificing metal to be leached out such as Zn or Al together with Ni or the like on a substrate, and leaching out and removing the sacrificing metal to form a porous coating of Ni or the like on the substrate (e.g., as disclosed in, e.g., Japanese Patent Publication No. 6611/56 and Japanese Patent Applications (OPI) Nos. 54877/76 and 36583/77); a method comprising coating an alloy such as a Ni-Mo alloy on a substrate [e.g., as disclosed in British Pat. No. 992,350 (corresponding to Japanese Patent Publication No. 9130/65)]; and a method comprising coating a platinum-group metal oxide or a mixture thereof with another metal oxide (e.g., as disclosed in Japanese Patent Applications (OPI) Nos. 131474/76 and 11178/77).
These conventional cathodes can be expected to provide a considerably reduced hydrogen evolution potential. Although their durability is to some extent feasible under relatively mild conditions as in the conventional diaphragm-method electrolysis of an alkali metal halide, such as sodium chloride, they do not have satisfactory durability under the severe conditions encountered in the ion exchange membrane-method electrolysis of an alkali metal halide, such as sodium chloride, which has been employed in recent years.
In the electrolysis of an alkali metal halide, such as sodium chloride, using an ion-exchange membrane method, the cathode is exposed to a high-temperature, high-concentration sodium chloride solution (usually at about 80.degree. to about 100.degree. C. with a concentration of more than about 25% by weight). Accordingly, the substrate of the cathode tends to be corroded gradually, and this leads to electrode damage even when the cathode has a corrosion-resistant activating cathode coating and is loaded with a negative potential as a cathode.